Carrier for test, burn-in, and first level packaging

ABSTRACT

A plurality of semiconductor devices are provided on a carrier for testing or burning-in. The carrier is then cut up to provide single chip-on-carrier components or multi-chip-on-carrier components. The carrier is used as a first level package for each chip. Thus, the carrier serves a dual purpose for test and burn-in and for packaging. A lead reduction mechanism, such as a built-in self-test engine, can be provided on each chip or on the carrier and is connected to contacts of the carrier for the testing and burn-in steps. The final package after cutting includes at least one known good die and may include an array of chips on the carrier, such as a SIMM or a DIMM. The final package can also be a stack of chips each mounted on a separate carrier. The carriers of the stack are connected to each other through a substrate mounted along a side face of the stack that is electrically connected to a line of pads along an edge of each carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application under 35 U.S.C. 121 ofco-pending U.S. patent application Ser. No. 09/588,617, filed on Jun. 6,2000, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to an improved method of semiconductortesting, burning-in, and packaging.

Both standard module burn-in and wafer burn-in schemes are wasteful oftime space and resource. Module burn-in requires dicing, bond, assembly,and test before burn-in, adding considerable expense to modules thatfail burn-in. Wafer burn-in permits burn-in before dicing, saving thepackaging cost for failing chips, but it obviously requires theinclusion of the failing chips on the wafer in the burn-in apparatus.Provision must then be provided for disconnecting shorted chips orhandling very high currents while providing voltage uniformity. Thus,wafer burn-in is most cost effective for high yielding wafers.

Chip or die burn-in schemes like IBM's R3 process and TI's Diemateprocess avoid the packaging steps required by module burn-in. Onlytested bare chips are burned-in. The R3 process permits simultaneousburn-in of a large array of chips. The chips are solder bump mounted ona ceramic substrate which can be reused a number of times. This providesadvantage over the Diemate process which burns in only one chip at atime in each fixture. But the cost of the R3 process can still beexpensive since the substrate can only be reused about ten or twentytimes. And there is substantial cost for aligning and attaching chips tothe substrate and then for removing them and preparing them forreattaching to a final substrate once burn-in is complete. Therefore thecost of producing known good die with module burn-in, wafer burn-in, theR3 process, or the Diemate process can be quite high. Thus, a bettersolution for test and burn-in is needed that lowers the cost, and thatsolution is provided by this invention.

SUMMARY

The present invention provides a method for manufacturing and testingsemiconductor components that combines testing, burning-in, andpackaging. The method includes the step of providing a plurality ofsemiconductor devices and a device carrier. The carrier has interconnectwiring therein sufficient for both testing and end use operation of thesemiconductor devices. The semiconductor devices are attached to thecarrier. The devices are then tested via the wiring in the carrier. Thecarrier is then divided up into a plurality of components such that eachcomponent contains at least one semiconductor device. Those components,including the carrier are used as the first packaging level of assembly.

In another aspect, the invention provides a semiconductor structurecomprising a device carrier. The carrier has interconnect wiring thereinsufficient for both testing and end use operation of the semiconductordevices. A plurality of semiconductor devices are mounted to thecarrier. The devices on the carrier may be tested and burned-in and thecarrier may be divided into a plurality of components, and thecomponents may be installed in an information handling system withoutseparating the devices from the carrier.

In another aspect, the invention provides a semiconductor structurecomprising a stack of flex device carriers. At least one semiconductordevice is mounted to each of the flex carriers. Each of the flex devicecarriers is in turn connected to an interconnect substrate tointerconnect the devices. The substrate can be used for externalconnection or for connection to an additional chip or chips.

Still other objects and advantages of the present invention will becomereadily apparent by those skilled in the art from the following detaileddescription, wherein it is shown and described only the preferredembodiments of the invention, simply by way of illustration of the bestmode contemplated of carrying out the invention. As will be realized,the invention is capable of other and different embodiments, and itsseveral details are capable of modifications in various obviousrespects, without departing from the invention. Accordingly, thedrawings and description are to be regarded as illustrative in natureand not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and advantages of the present invention willbe more clearly understood when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 a is an exploded perspective view of two chips mounted on acarrier that is used for test, burn-in and packaging;

FIG. 1 b is a perspective view of another embodiment of a multi-functioncarrier according to the present invention;

FIG. 2 a is a perspective view of a plurality of multi-function carrieraccording to the present invention engaged in an embodiment of a burn-intray according to the present invention;

FIG. 2 b is a perspective view of the embodiment of a multi-functioncarrier according to the present invention with a plurality ofsemiconductor chips attached thereto;

FIG. 3 is a perspective view of an embodiment of a multi-functionpackage according to the present invention illustrating removal of aportion of the carrier subsequent to carrying out processing on thecarrier;

FIG. 4 is a view of another embodiment of a multi-function packageaccording to the present invention;

FIG. 5 is a perspective view of another embodiment of a multi-functionpackage according to the present invention, including encapsulant aboutthe semiconductor chips;

FIG. 6 is an overhead view of the embodiment of a multifunction packageshown in FIG. 5, illustrating cutting of the package;

FIG. 7 is a cross-sectional view of another embodiment of amulti-function package according to the present invention;

FIG. 8 is an overhead view of another embodiment of a multi-functionpackage according to the present invention;

FIG. 9 a is a portion of a multi-functional carrier according to thepresent invention;

FIG. 9 b is an overhead view of another embodiment of a multi-functionalcarrier according to the present invention;

FIG. 10 is an overhead view of another embodiment of a multi-functionalcarrier according to the present invention;

FIG. 11 is an overhead view of another embodiment of a multi-functionalcarrier according to the present invention;

FIG. 12 is a three dimensional view of an arrangement for at-speedtesting and burning in of an array of chips involving a flex connectorfor the array of chips and a second board for providing regulated powerto the chips;

FIG. 13 a is a side view of a stack of chips formed by connecting aplurality of components to a substrate; and

FIG. 13 b is a side view of the stack of chips of FIG. 13 a.

DETAILED DESCRIPTION

As performance of semiconductor chips increases, testing and burn-in andthe above-discussed problems may find even greater significance. Alongthese lines, there is a push for high performance logic and memorychips. Low inductance connections to DRAM chips, for example, aredesired to achieve high performance, along the lines of about 200 MHz toabout 500 MHz or greater. Thin small outline packages (TSOP) and smalloutline J-lead (SOJ) packages typically have inductances ranging fromabout 5 to about 9 nanohenries (nh). Flip-chip packages with solderbumps, such as C4, stud bumps, and others, have inductances of less thanabout 0.5 nh, and these chips are finding increasing use in theindustry. Burn-in is costly for solder bump attached chips. Wafer levelburn-in and temporary chip attach (TCA) approaches to test and burn-inare expensive.

The present invention provides a new approach to the die or chip burn-inprocess. An array of chips are mounted on a carrier for test andburn-in. The carrier is then divided up and used as the final substratefor packaging. Advantages of the present invention include providing alow cost solution for burning-in and packaging chips by combining theburn-in substrate and the final substrate. Along these lines, a burn-in“vehicle” according to the present invention may be later reused as-isto become a final package. The package may contain single chips, stackedchips or an array of chips or stacked chips. The package may be a chipscale package.

Several additional advantages are inherent in the present invention.Redundancy may be invoked after burn-in. Therefore, fewer chips onmulti-chip modules need be replaced after test or burn-in. Further costreduction and time and material savings can be realized in theelimination of a level of wire bonding. C4 bonding also provides higherperformance. Elimination of a level of wire bonding can permit a packageaccording to the present invention to be used at frequencies of 200 MHzand above.

Particularly in the context of memory chips, the present invention canpermit a memory product card, such as a SIMM, DIMM, PCMCIA, or other, tobe used to carry out a burn-in and a final module test. With a flip-chipDRAM, for example, both burn-in and final testing may be carried out onthe same card. Attach techniques according to the present inventionpermit carrying out of several reworks to permit replacement for DRAMchip fallout during burn-in and final card test. The attach techniquesfurther permit card repair due to failure in a computer afterinstallation of the card in the computer.

While the present invention works with flip-chips, it also works withchips mounted with other techniques. For example, the present inventionmay be used with wire bond mounted bare dies. The present invention mayalso be used with chip scale packages (CSP) and TSOP/SOJ modules ifthere is a rework process for detaching and re-attaching modules to aSIMM or other memory card.

Broadly, a method according to the present invention includes providingat least one semiconductor device on a semiconductor carrier. Typically,a plurality of semiconductor devices are attached to the carrier. Thesemiconductor devices may be memory chips, logic chips, or othersemiconductor devices. Along these lines, the present invention may beused with any semiconductor device that is attached to a substrate forcarrying out processing, such as burning-in and testing.

According to the present invention, the testing circuitry may be builtin to the chips. Along these lines, each chip may have a built in selftest (BIST) engine incorporated into its design. The BIST engines mayinclude a wide range of capabilities. For example, by including a BISTengine, a memory chip may be tested at speed, with the exception ofreceivers and drivers, which may be tested as part of the performance ofa card assembly. However, it is not necessary that a chip include a BISTengine. The test engine can be included on the carrier as a separatedevice from the chips being tested. The test engines could also belocated on a separate card. Alternatively, test signals and patterns canbe generated by an external tester.

A simple BIST engine can provide patterns for burn-in and for final chiptesting at speed. The testing may be extensive, testing forfunctionality, sensitivities, and other characteristics. The testing maybe performed before wafer level fuse blowing, bumping and dicing. Asimple BIST engine may be very small, the chip area increases by about3% or less to accommodate the BIST engine. In the future, it is expectedthat the BIST engine will be incorporated into different kinds of chips,such as DRAM, SRAM, Flash memory, EEPROM, and other types, as a way toreduce cost from test and burn-in.

A more complex BIST engine may include complex patterns or performredundancy calculations, among other tasks. However, such a BIST enginemay have a greater area penalty on the chip than other, simpler BISTengines. Along these lines, the area impact may be greater than about3%. A productivity penalty may also be associated with the additionalfunctionality.

Additional leads are provided for connecting the BIST engine to signalsources, such as power and ground. According to typical embodiments, achip may include 5 or 6 extra leads for the BIST engine. However, anynumber of leads may be included as necessary to accommodate the BISTengine. A carrier that the chips are attached to includes a number ofpads corresponding to the number of leads on the chip for the BIST. Thepads may be provided for an entire memory card or board or SIMM or othermemory structure. The pads permit connection to the BIST leads for testand burn-in. The BIST engines may be connected in series to the extrapads. Alternatively, pads may be provided for separate portions of amemory card or board. For example, pads for a separate BIST engine canbe provided for each SIMM or DIMM portion of the card, as shown in FIG.11.

Providing separate pads and BIST engines for each group of devices on aboard would provide greater parallel reading of data from devices duringburn-in, and this reduces the overall time needed for burn-in.

The semiconductor devices are attached to the carrier using anattachment scheme such as controlled collapse chip connections (C4),solder columns, wire bonds, or conductive adhesive. C4 connections orother connections may be used to attach chips or other devices toopposite sides of the carrier. The carrier can also have tester chipscomprising BIST engines and pads for external connection, such as edgeconnectors.

FIG. 1 a illustrates semiconductor devices in the form of two memorychips 1 and 3 being attached to a carrier. The bottom chip 3 shows C4connections 5 for a functional portion 7 of the chip. The chip 3 alsoincludes C4 connections 9 for an on-chip BIST engine 11. As statedabove, inclusion of the on-chip BIST engine is an option.

In the embodiment shown in FIG. 1 a, the carrier 12 is made of polyimideor other equivalent flex carrier material. The carrier can also be madeof ceramic FR-4 laminate, or other suitable material. The carrier mayhave provision for being segmented after testing and burn-in arecomplete.

The carrier shown in FIG. 1 a includes C4 pads 13 for connection to theC4 connections on the chips. Leads 15 are connected to the C4 pads 13and extend away from the pads. The embodiment of the carrier alsoincludes C4 pads 17 for connection to the C4 connections on the BISTengine on the chips. Leads 19 extend away from C4 pads 17. All of theleads 15 and 19 on the embodiment of the carrier shown in FIG. 1 aterminate in a tab 21.

FIG. 1 b illustrates another embodiment of a carrier 23 according to thepresent invention. The carrier 23 shown in FIG. 1 b is a flexiblemini-ladder carrier that can accommodate a plurality of semiconductordevices thereon. Including multiple sets of chips or other semiconductordevices on one carrier, such as a flexible card, for example themini-ladder shown in FIGS. 1 b, 2 a, and 2 b, can increase manufacturingefficiency. Along these lines, multiple chips on one carrier can reducehandling and test set-up time and cost, permitting multiple modules tobe delivered for testing at one time. This typically is not possiblewith singulated TSOPs or SOJs.

As such, the carrier 23 includes C4 pads 25 for connecting to C4connections on the devices to be attached to the carrier. The carrier 23also includes leads 27 attached to C4 pads 25 and tabs 29 extending fromthe leads. Also, similar to the embodiment represented in FIG. 1 a, theembodiment of the carrier shown in FIG. 1 b includes C4 pads 31 forattaching C4 connections of the BIST engines of the attachedsemiconductor devices. Leads 33, which terminate in tabs 35, extend frompads 31.

FIG. 8 illustrates another embodiment of a carrier according to thepresent invention with attached semiconductor devices. In particular,FIG. 8 shows multiple SIMM's 100 attached to a card 102. Each SIMMincludes 9 attached chips 104. The chips 104 are attached with flip-chipattachments. Along these lines, FIG. 8 illustrates solder bumps on eachchip 104. If semiconductor devices are attached to both sides of thecarrier 102, then 54 flip-chips could be attached to the embodiment ofthe carrier illustrated in FIG. 8.

A plurality of decoupling capacitors 106 may be provided on a carrier,as shown in FIG. 8. The decoupling capacitors may be used for powersupply and ground decoupling on the semiconductor devices attached tothe carrier. As such, the capacitors may be available for burn-in andfinal memory card test of the final assembly. The capacitors may be usedfor all SIMM or other memory cards.

FIG. 9 b illustrates an embodiment of the present invention wherein theattached semiconductor devices each include a BIST engine. Along theselines, FIG. 9 b shows a SIMM or DIMM card 112 with attached chips 114.The chips may be memory or logic chips. The chips 114 may be attached tothe card with flip-chip connections as evidenced by solder bumps 116.

As previously stated, each chip includes a BIST engine. As such, eachchip includes solder bumps 118 for connection of the BIST engines. Lessthan ten external contacts for making contact to and controlling theBIST engine are needed. These are in addition to the contacts to chippads that will be used during normal operation of the chip. SIMM or DIMMBIST wiring 120 is included for connecting the BIST engines to BISTconnections 122 on the card. The BIST engine includes five connectionslabeled 1 through 5 on the chip illustrated in FIG. 9 a. The BIST enginecan include connections for clocks that provide scan in vectors or testpatterns and that clock and run the BIST engine. Connections can also beprovided for scan-in and scan-out. The semiconductor devices attached tothe carrier may be connected in parallel to the external contacts.

The carrier 112 illustrated in FIG. 9 b includes a SIMM or DIMMconnector 124 at one side of the card.

FIG. 9 a illustrates one of the chips shown attached to a carrier 112shown in FIG. 9 b. As previously mentioned, the chip may be a memory orlogic chip. The chip shown in FIG. 9 a includes the BIST engine. Also,FIG. 9 a illustrates the solder connections for connecting the chip tosites on the carrier.

FIG. 10 illustrates an embodiment of a multi-function package accordingto the present invention that includes a plurality of semiconductordevices that each includes a BIST engine. Along these lines, FIG. 10illustrates a carrier 126 with a plurality of chips 128 attachedthereto. The chips 128 are attached to the carrier 126 with solder bumps130.

The BIST engines on each chip are connected to pads 134 on carrier 126through solder bumps 132 and BIST wiring connectors 134. Additionally,each BIST connector 134 connects the same solder bump on eachsemiconductor device 130 attached to the carrier, thereby connectingeach similar bump 132 on a semiconductor device to one of the BIST pads.As such, corresponding solder bumps on each semiconductor device areconnected in common.

The carrier illustrated in FIG. 10 also includes power supply (Vps)connections 138 and ground (Gnd) connections 140. At least one set ofvoltage and ground connections is provided for each set, in this caseeach row of semiconductor devices.

Additionally, a set of connectors 142 is also provided for each set ofsemiconductor devices. Connectors 142 will permit the sets ofsemiconductor devices to be connected to a computer or in anotherapplication after the sets of semiconductor devices are separated. Theseconnectors are similar to the connectors 124 in the embodimentillustrated in FIG. 9 b. As can be seen in FIG. 10, the BIST connectionsare separate from the semiconductor device connections.

In FIG. 10, the three sets of semiconductor devices may each be a SIMM.In other words, FIG. 10 illustrates a three SIMM ladder. In the stateillustrated in FIG. 10, there typically is no need to make connection tothe SIMM connectors 142 during burn-in and for high speed memorytesting. Such an embodiment does not require additional connections onthe SIMM.

Assembling multiple sets of semiconductor devices on a single carrier,such as a flexible card, can reduce product handling and set up time andcost. Additionally, multiple modules may be delivered for test at onetime.

After connection of one or more semiconductor devices to a carrier,burn-in, testing, be carried out on the semiconductor device(s) attachedto the carrier. The burning-in and testing may be carried out on thesemiconductor devices simultaneously. Also, the burning-in and testingmay or may not be carried out on the semiconductor devices independentlyof each other.

Carrying out burn-in, testing, and/or other functions typically includesexposing the carrier and attached devices to temperature and voltageconditions necessary for the testing or burn-in. The present inventionpermits this processing to be carried out on the carrier that will thenbe installed in a computer or other application. The carrier may bemodified as described below prior to final installation.

FIG. 2 a illustrates an example where carriers 23 with semiconductordevices 37 attached are arranged in a tray 39 for carrying outprocessing. The embodiment of the tray 39 shown in FIG. 2 a is forburn-in and for receiving carriers capable of having attached theretosemiconductor devices that include BIST engines. The tray illustrated inFIG. 2 a includes three slots 41 for receiving carriers. FIG. 2 billustrates a carrier in the process of being inserted into one of theslots 41.

The tray includes contacts 43 for contacting the connection leads/tabson the carrier 23. If no BIST engines were included, standardinput/output pads typically are used to make contact for burn-in andtesting. Rather than being inserted into a carrier, probes may beattached to the I/O pads for carrying out the burn-in and testing.

After burning-in, a “singulation” process may be carried out. Thecarrier is cut into individual chips or multi-chip components. If a BISTengine was included as a separate chip on the carrier the portion of thecarrier containing the BIST engine can be cut off as well. The carrieris FIG. 3 illustrates this process. In FIG. 3, a blade may be used tocut off a portion of the carrier to provide a multi-chip component. Thebroken line 47 illustrates where the blade will sever the carrier.Broken line 49 illustrates the final position of the blade 45 aftercutting the carrier.

According to the embodiment illustrated in FIGS. 1-3, functional testingmay be carried out on singular packages, such as the portion of thecarrier remaining after the cutting of the carrier step shown in FIG. 3.Manufacturing efficiency may be enhanced by utilizing mini-ladders, suchas that illustrated in FIGS. 1 b, 2 a, 2 b, and 3 if the tester/sorterequipment employed includes trimming and sorting equipment driven bytest results. At this time, failing dies on each multi-chip componentmay be reworked if necessary. If the carrier is cut so as to provideindividual dies mounted on carrier, then any carrier pieces having diesthat cannot be repaired by invoking redundancy are scrapped. Theremainder, having passed test or burn-in, are considered known good diemounted on a first level package.

Flex or microflex may also be used as a carrier to provide a highdensity array of chips for burn-in. One or two level wiring in the flexconnects the chips to large pads on the periphery of the flex forcontact during burn-in. Electrically blown fuses may be integrated intoone conductive level of the flex to automatically disconnect chips thatshort during burn-in. The other conductive level of the flex may havethick wiring, from 0.5 to 2 mils thick or thicker, providing a lowresistance path so high current at uniform voltage can be provided toall chips. The chips may be mounted to the flex using standard C4 orwire bonds.

Contacts to the large pads on the flex permit testing with a standardburn-in tester. Tester chips may be located on a board near the flex ina lower temperature environment. The tester chips include test circuitsand voltage regulators to ensure voltage control and uniformity.Alternatively BIST engines may be provided on each chip. In anotheralternative, the flex can also include small tester chips with testcircuits to provide test signals as described herein. Voltage regulatorscan also be provided on the flex to ensure that each chip is receivingthe correct stress voltage regardless of current drawn, as described incommonly assigned U.S. Pat. No. 5,600,257, incorporated herein byreference.

Preferably, contact pads are located along at least one edge of the flexwith wide thick lines for power and ground along with the small numberof bused I/O lines needed for testing on one conductive level of theflex. Contact pads can also be located between chips, and these pads canlater be used for wire bond connections to the next level of assembly.Alternatively, contact pads can be located on the side of the flexopposite the chips. In this embodiment, each chip on the flex can beseparately probed. The pads on the opposite side of the flex can be muchlarger than chip contact pads. The pads can be used for connection tothe next level of assembly, so the flex provides both a burn-in vehicleand a chip scale package.

After burn-in chips are repaired by invoking redundancy by laser blowingfuses. The fuse blow step can also be used to personalize the chip for aspecific function. For C4 chips, laser energy is applied through thetransparent flex or through a window previously cut in the flex abovethe fuse bay region on the chip. For wire bond chips the active surfaceand fuses are accessible directly. Thus, many burn-in fails are easilyrepaired. The present invention provides significantly enhancement sinceit takes further advantage of the flex for test, burn-in and fuse blowto repair what would otherwise be burn-in fails. All chips on the flexcan then be tested. The flex is then cut or diced to provide individualflex mounted chips. Passing chips, already mounted on flex, are readyfor the next level of assembly which can be a lead frame, a PC board, ora chip stack. Thus, chips are preferably not removed from the flex afterburn-in; the flex provides significant advantage for a variety ofpackaging solutions.

The flex burn-in has several advantages over wafer burn-in: chip scaleflex burn-in apparatus is significantly lower cost than wafer burn-inapparatus since contact to large pads on the flex eliminates theexpensive thermally matched prober needed for wafer burn-in. It alsolowers burn-in cost since it has approximately the same chip density aswafer burn-in but only good chips are burned-in. Hence the good chipdensity can be much higher than available in wafer burn-in. In additioncomplications from shorted chips are mostly avoided. Shorted chips arethrown away after dicing, are not connected to the flex, and are notburned in (though provision for chips that short during burn-in isprovided by fuses included in the flex). Similarly, using a singlecarrier such as flex for burn-in and packaging is also substantiallycheaper than older chip scale burn-in such as the R3 or Diemate methodsof chip burn-in which must be followed by a separate packaging step. Theresult is a known good die or known good multi-dies in a package readyfor the next level of assembly.

The scheme has several other advantages as well. It provides a low costscheme for at-speed test and for burn-in through a low cost first levelpackage. The carrier provides an interface that avoids any need tochange chip or wafer design or process for testing an array of chipssimultaneously. It provides heavy wiring to provide very large currentfor parallel test and burn-in of the large array of chips whileproviding voltage regulators that sense and provide precise voltage ateach chip for test. It also provides a way to automatically disconnectshorted chips. The flex provides a low cost scheme for addressingthermal mismatch since flex is compliant. On board self-test enginesreduce testing time by providing for parallel test. Programmableself-test engines can also give repair instructions. The scheme issuperior to wafer burn-in, particularly for low yield wafers or theearly learning portion of a program since only good chips are picked formounting on the carrier for further test and burn-in. If the testengines are off chip they can be kept out of the hot zone duringburn-in, avoiding burning in self-test engines. The known good dieresulting from the scheme are ready for dense packaging, such as stacksof chips.

One embodiment of a scheme for at-speed wafer test and burn-in is testhead 220 shown in FIG. 12. All chips mounted on the bottom surface offlex 222 are contacted with probes 276 extending through plastichousings 278 held in frame 280 that connect pads 262 a on flex 222 topads on second board 224. Second board 224 carries tester chips 228 onits top surface 270, as described in wafer burn-in U.S. Pat. No.5,600,257, incorporated herein by reference. Second board 224 can be aprinted circuit board. Tester chips 228 include (1) tester circuits(BIST) and (2) voltage regulators. In addition to lines extending fromthe voltage regulators to the chips under test that provide power andground, the voltage regulators have additional isolated contacts to thechips under test to sense the on-chip voltage of each chip under test.The voltage regulators can then regulate the measured chip voltage to areference voltage to ensure that the actual chip voltage equals thereference voltage for precise test. Thus, variation in voltage todifferent chips from variation in current drawn can be eliminated.Voltage regulators can also be used to disconnect or limit current toshorted chips. In this embodiment, second board 224 has thickmetallization to carry large currents needed by the voltage regulatorson the tester chips and to provide current from the voltage regulatorsto the chips under test. Second board 224 holding tester chips 228 isgeneric for all chips in a product family while flex 222 has a contactpad scheme specific for the chips under test.

In this embodiment flex 222 need not have thick wiring to carry largecurrent since second board 224 performs that function. Flex 222 has padson both sides. Top side 260 of flex 222 has the generic layout neededfor contact with second board 224 carrying tester chips 228. Pins 276are used for connection between the boards The bottom side of flex 222has pads arranged to mate with pads on the chips under test. Inaddition, both flex 222 and second board 224 can carry decouplingcapacitors needed for the at-speed testing. In this embodiment testerchips may be kept at a lower temperature than chips under test. If BISTengines are provided on each chip under test, the scheme can still beused to provide regulated voltage to each chip.

In one embodiment of a packaging scheme, the next level of assembly iscompact stack of chips 200, as shown in side and top views in FIGS. 13a, 13 b. Stack 200 can be assembled by stacking known good chips 201mounted on flex 202. Each flex 202 has wiring 204 connecting pads 206 onflex 202 and chip 200 to pads 208 along edge 210 of flex 202.Interconnect substrate 212 is electrically connected to each edge pad208 to provide interconnection among stacked chips 201. Interconnectsubstrate 212 can be a flex, PC board, ceramic substrate, or asemiconductor chip. Other chips, such as chip 201′, may be mounted tointerconnect substrate 212. Interconnect substrate 212 can also havepads 214 for external connection to stack of chips 200. The structurecan be used, for example, to provide a large number of memory chips ascache for a microprocessor mounted on interconnect substrate 212. Solderbumps provided by wave soldering can be used at the pads 208 at the endof each wire 204 on flex 202 for connection with interconnect substrate212. Alternatively, flex 202 can plug into connectors on interconnectsubstrate 212. Copper plates (not shown) can be provided between flex202 layers to provide for heat removal. In this stacked arrangement flex202 and interconnect substrate 212 provide all wiring interconnectionamong chips of the stack and for external connection without the need toprovide any additional wafer or stack processing beyond connecting chipsto flex and flex to substrate.

FIG. 4 illustrates a carrier 51 such as that shown in FIGS. 1-3 in theprocess of undergoing a functionality test. The carrier is beingcontacted by a po-go array 53. The po-go array contacts the contactregions on the carrier that extend from the connections pads on thecarrier that the chips are attached to. The arrangement illustrated inFIG. 4 may also be used for burn-in and testing if the BIST engine isnot included on the chips or not used.

After burn-in and testing, the chips may be encapsulated. Encapsulationmay be accomplished by placing a conformal coating all around the edgesof the chips. The coating may be on both sides of the carrier if chipsare attached to both sides. FIG. 5 illustrates a portion of a carrierwith a coating 55 around the chips on the carrier.

Portions of the carrier with individual chips may be separated from eachother prior to or after the encapsulation. The carrier may be cututilizing any suitable method and apparatus. FIG. 6 illustrates aportion of the carrier with a chip attached. A chip may also be attachedto the other side of the portion of the carrier shown in FIG. 6.

Any embodiment of the present invention may also include a temporarycover for covering the chips during handling for burning-in and testing.Permanent covering or encapsulation may then be placed on the carrierfor more permanent protection.

To attach the flex to another carrier, such as a printed circuit board,in a manner similar to the attachment of a standard surface mountcomponent, such as a lead frame or TSOP, it is desirable to separate theleads in the attachment region so they simulate the leads of a leadframe or TSOP. FIG. 6 illustrates locations 57 where the carrier may becut. The portions of the carrier shown in FIG. 6 may then beincorporated into another structure.

FIG. 7 illustrates two carrier portions 59 and 61 attached to thesurface of a substrate 60. Any substrate may be used to attach thecarrier portions 59 and 61 to. According to one example, an FR-4 carriermay be used. Other examples include ceramic carriers and organic orother laminate carriers. Each carrier portion 59 and 61 has chips 59 aand 59 b and 61 a and 61 b attached thereto. The leads and tabs 59 c and61 c portions of the carrier portions 59 and 61 are actually attached tothe substrate 60. It is not necessary that a carrier portion be attachedto both sides of the substrate.

The embodiment of the present invention illustrated in FIGS. 8-10undergoes similar processing to that described above. An embodiment ofthe present invention illustrated in FIG. 8 could be placed in a burn-inoven with connections (not shown) to each connector on the carrier. Thedevices, SIMM's in this case, may be monitored in situ during burn-in.During this time, failing modules are identified. Burn-in fallout for amature program may be about 1% to about 2%. Chips falling out arereplaced prior to shipment of the SIMM to a customer. As stated above,one of the advantages of the present invention is that the chips may beburned-in and shipped without being detached from the carrier, exceptfor failing chips, which are replaced.

For an embodiment of the present invention, such as that illustrated inFIGS. 9 a and 10, which include BIST engines, the burn-in and testsequence may be as follows. A wafer level test and fuse blow may becarried out. Good chips may be picked and connected to the carrier, suchas a SIMM, DIMM, PCMCIA or other memory card, by C4 connections. Apre-burn-in test may then be carried out using the BIST engines, ifrequired.

Next, the carriers and attached chips may be place in a burn-in chamber.The chips may be put in a burn-in mode using initialization program (IP)codes. The BIST engines can supply the patterns and record failures ofthe chips.

All chips attached to the carrier(s) receive the full insitu burn-incycle including 140° C. reliability stressing, 85° C. sensitivitytesting and temperature ramp-up/ramp-down exposure tests. During thetesting, all chips operate in parallel. At the end of the testing, theBIST engine chains are read out. The chains identify failing chiplocations. In addition, the full assembly of chips and carriers can thenbe tested at full function and speed after burn-in is complete using theBIST engine and/or using memory function tests applied to the connectorson the carriers. Data for both the burn-in and memory testing may becombined. Failing chips may then be replaced with good chips in a reworkstep.

Preferably, chips used to replace the failed chips in the rework stepare fully burned-in and tested chips from another card. Afterreplacement with previously burned-in chips, only a final test of thememory card is needed.

Alternatively, the memory chips used to replace failed chips in therework cycle may be new, non-burned-in chips. In this embodiment of thepresent invention, the memory assembly may again be placed in a burn-inoven and retested after burn-in is complete.

Replacement and reburn-in are not required if the carrier is singulatedinto single chip components. Failing components are discarded, andpassing components are identified as known good die.

Once all chips are identified as good using the BIST engines, a finalmemory application function may be tested at speed. Such testingtypically does not employ the BIST engine. The BIST engines may be usedto test all memory chips on a memory card, at speed, in parallel, exceptfor the final test in chip receivers and drivers, which may be tested aspart of the final assembly. After any final testing, the product maythen be shipped to customers.

Memory chips attached to a carrier according to the present inventionmay be tested at full functional speed using the BIST engines. The BISTengines can be used in the system as part of the system diagnostics whensystem memory fails if included as part of the SIMM system design. Asystem can identify a bad memory chip or chips and send data along withthe SIMM, DIMM, or other memory assembly to the factory. The system cantest spare chips on the memory card using the BIST engine and thensubstitute good chips for bad chips in the system. The checking andsubstitution can be transparent to the application.

The present invention can provide a relatively simple, portable systemfor carrying out field tests, burn-in and repair for systems thatinclude memory chips that include BIST engines and access to the BISTengines. Although the above example includes DRAM's, the system willwork with SRAM's, logic with memory macros, logic, EEPROM, flash, andother applications.

To enhance the thermal properties of a multi-function assembly accordingto the present invention, a copper backing sheet may be added to thecarrier. The copper backing sheet may be attached to an external heatsink and/or fins. The copper backing sheet may also or alternatively beattached to a printed circuit board (pcb) that the carrier is attachedto. Thermal management may also be accomplished by removing heat fromsides of a carrier not used for electrical connection.

Other enhancements that may be made to the carriers described aboveinclude providing for electrical connection to more than one side of achip. This technique may be used to segregate next level assemblyinterconnection from burn-in and test interconnection.

A window can be provided in the flex to enable accessing fuses for fuseblow or fuse testing. Because the fuses remain accessible through thewindow, the structure allows invoking redundancy and blowing fuses afterburn-in is complete to repair defects produced by burn-in. For C4mounted chips, a window may be present in a carrier, such as a flex,that the chips are mounted to for access to a portion of the activesurface of the chip, such as fuse bays. A window can also enableproviding a chip-on-chip structure, in which the smaller chip is locatedin the window in the flex. For wire bond and flip chips the activesurface and fuse bays may be accessible. In such cases, an opening or“window” may exist in the chip carrier that permits access to activeregions of a chip. This can permit use of laser or other tools to modifycircuitry, such as via fuses. The capability to invoke redundancy postburn-in can result in significantly higher product yield and lower cost.

A flex carrier may be used to personalize a chip. Along these lines,utilizing selective laser deletion on the flex, changes can be effectedon chip function. This can be accomplished at the same time that chipfuse laser deletion is carried out.

The foregoing description of the invention illustrates and describes thepresent invention. Additionally, the disclosure shows and describes onlythe preferred embodiments of the invention, but as aforementioned, it isto be understood that the invention is capable of use in various othercombinations, modifications, and environments and is capable of changesor modifications within the scope of the inventive concept as expressedherein, commensurate with the above teachings, and/or the skill orknowledge of the relevant art. The embodiments described hereinabove arefurther intended to explain best modes known of practicing the inventionand to enable others skilled in the art to utilize the invention insuch, or other, embodiments and with the various modifications requiredby the particular applications or uses of the invention. Accordingly,the description is not intended to limit the invention to the formdisclosed herein. Also, it is intended that the appended claims beconstrued to include alternative embodiments.

1. A semiconductor structure comprising: a stack of flex devicecarriers, wherein at least one semiconductor device is mounted to eachsaid flex device carrier; and an interconnect substrate, wherein saidflex device carriers are electrically connected to said interconnectsubstrate.
 2. The semiconductor structure of claim 1, wherein said stackof flex device carriers, said at least one semiconductor device, andsaid interconnect substrate are interconnected and arranged in a mannersuitable for both operational testing and packaging of the semiconductorstructure.
 3. The semiconductor structure of claim 1, wherein each saidflex device carrier is arranged to be divided into a plurality ofcomponents, and wherein said plurality of components are arranged so asto be suitably installed in an information handling system withoutseparating said at least one semiconductor device from said flex devicecarrier.
 4. The semiconductor structure of claim 1, wherein each saidflex device carrier comprises contacts for external connection, saidstructure further comprising a lead reduction mechanism on each saidflex device carrier, said lead reduction mechanism connected to saidcontacts of said flex device carrier.
 5. The semiconductor structure ofclaim 1, wherein each said flex device carrier comprises interconnectwiring therein sufficient for both testing and packaging of said atleast one semiconductor device.